Dedeleco you told me about hysteresis, about the demagnetization of the magnet when the coil becomes strongly magnetic, you can give me the formulas to use
The formulas are those on:
a) properties of the magnets:
http://fr.wikipedia.org/wiki/Aimant_permanent
http://fr.wikipedia.org/wiki/Magn%C3%A9tisme
http://en.wikipedia.org/wiki/Magnetism
http://en.wikipedia.org/wiki/Supermagnet
http://en.wikipedia.org/wiki/Magnet
http://en.wikipedia.org/wiki/Inductor
finally the field created by a coil is:
http://fr.wikipedia.org/wiki/Spire_de_courant
56 turns with 20A on a diameter of 3,6cm give 32KA / m which must be much lower than the coercive field of 862KA / m (fairly well checked), because otherwise the magnet is demagnetized.
So that will not happen but there is a weak hysteresis cycle around the residual field, which will heat up a bit, but there is not enough information to calculate.
Also since the magnet is conductive, there are eddy currents in it which heat it up a bit.
Hazard :
How to remove a finger with two super magnets
http://scienceblogs.com/sciencepunk/200 ... ith_tw.php
Do you know how to know if the section of the wire is too large compared to the density of the flux of the magnet?
The wire section has no direct relationship with the magnet.
The section of the wire fixes its resistance for the length of the wire, which determines the current in short circuit and the power dissipated in the wire of the coil, but the residual induction fixes the induced voltages
We calculate it with:
http://fr.wikipedia.org/wiki/R%C3%A9sis ... t%C3%A9%29
http://fr.wikipedia.org/wiki/R%C3%A9sistivit%C3%A9
A fairly similar study example in terms of methods on magnet motors:
http://artur.univ-fcomte.fr/ST/ELECTRO/ ... llegee.pdf